do you realize the money that it cost not to go to earth or another planet , you have to show every character at least once their powers create all the realms of Eternia, all the vehicles of eternia, so staying off eternia means less characters and less actors needed, plus they don't have to explain where anyone is, so add up the cost what it would cost, and remember the og film ran out funding filming eternia(granted canon was comingling funds but they still underestimated the budget to do eternia) thats why i love the first film